text: Excessive formation of the biological film may lead to certain problems such as sloughing, it is an important factor to maintain optimum biological film. Maintaining the biological film is accomplished by proper moisture content. For this purpose the humidity of the air is adjusted within the reaction chamber before the vapor flows over the packing media. The biological packing media may be natural or made of synthetic plastic. Recirculation of the water is always completed in the biological oxidation system to make the system more cost-effective. Biochemical oxygen demand (BOD) indirectly measures the amount of easily biodegradable organic matters thus very low values indicate direct waste water disposal.
  The prompt removal of a wide range of wastes and pollutants from the waste gas flow is the foremost requirement of biological oxidizers to meet regulatory permitting requirements. Micro-organisms differ in their ability to rapidly metabolize different pollutants, so the selection of the proper mix of organisms is critical. Research is underway to genetically modify various organisms to improve their performance in biological oxidation.